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1.
The genetic diversity and differentiation of four Zostera marina populations along the southern coast of Korea were estimated using random amplified polymorphic DNA (RAPD) markers to determine the effects of natural and anthropogenic stresses and reproductive strategy on within‐population genetic diversity. The mean number of alleles and gene diversities, indicating population genetic diversity, was highest in the Z. marina population that was exposed to repeated environmental disturbances, and lowest in the most undisturbed population. The higher genetic diversity in the disturbed population was associated with a higher contribution of sexual reproduction to population persistence. This suggests that both the level of disturbances and the reproductive strategy for population persistence contributed significantly to population genetic diversity at the study sites. According to the analysis of molecular variance (AMOVA), 76% genetic variation was attributable to differences among individuals within populations. The observed genetic differentiation (FST = 0.241) among Z. marina populations at the study sites appeared to result from reduced meadow size, increased genetic drift, and a high incidence of asexual reproduction. Increased population genetic diversity can enhance resistance and resilience to environmental disturbances; thus, this investigation of seagrass population genetics provides valuable new insights for the conservation, management, and restoration of seagrass habitats.  相似文献   

2.
Marine turtles are considered keystone consumers in tropical coastal ecosystems and their decline through overexploitation has been implicated in the deterioration of reefs and seagrass pastures in the Caribbean. In the present study, we analysed stomach contents of green (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata) harvested in the legal turtle fishery of the Turks and Caicos Islands (Caribbean) during 2008–2010. Small juveniles to adult‐sized turtles were sampled. Together with data from habitat surveys, we assessed diet composition and the taxonomic distinctness (and other species diversity measures) in the diets of these sympatric marine turtle species. The diet of green turtles (n = 92) consisted of a total of 47 taxa: including three species of seagrass (present in 99% of individuals), 29 species of algae and eight sponge species. Hawksbill turtles (n = 45) consumed 73 taxa and were largely spongivorous (16 species; sponges present in 100% of individuals) but also foraged on 50 species of algae (present in 73% of individuals) and three species of seagrass. Plastics were found in trace amounts in 4% of green turtle and 9% of hawksbill turtle stomach samples. We expected to find changes in diet that might reflect ontogenetic shifts from small (oceanic‐pelagic) turtles to larger (coastal‐benthic) turtles. Dietary composition (abundance and biomass), however, did not change significantly with turtle size, although average taxonomic distinctness was lower in larger green turtles. There was little overlap in prey between the two turtle species, suggesting niche separation. Taxonomic distinctness routines indicated that green turtles had the most selective diet, whereas hawksbill turtles were less selective than expected when compared with the relative frequency and biomass of diet items. We discuss these findings in relation to the likely important trophic roles that these sympatric turtle species play in reef and seagrass habitats.  相似文献   

3.
The growth dynamics of two co‐occurring seagrass species, Zostera marina and Halophila nipponica, were examined on the southern coast of the Korean peninsula. Zostera marina is a native dominant seagrass species in Korean coastal waters, whereas H. nipponica is a non‐native tropical and subtropical species that has extended its distributional range to the temperate coastal areas of Korea. To examine the differences in the growth dynamics of H. nipponica and Z.  marina, their morphology, density, productivity and biomass, as well as local environmental conditions, were monitored monthly from January 2008 to July 2009. Underwater irradiance at the study site was the highest in April 2009 and the lowest in January 2008. Water temperature ranged from 10.4°C in January 2009 to 24.8°C in September 2008. Significant differences in growth dynamics were observed between the species, due to the effect of water temperature at the study site. Density and areal productivity were the highest in April 2008 and June 2008, respectively, for Z.  marina but the highest in July 2008 for H. nipponica. Leaf size, shoot height and shoot weight were the highest in July 2008 for Z.  marina but the highest in August 2008 or September 2008 for H. nipponica. The productivity of both species was strongly correlated with water temperature at the study site. However, the productivity of these species was not strongly correlated with underwater irradiance or the nutrient availability of either the water column or sediment pore water. Zostera marina exhibited the ecological characteristics of a temperate seagrass, whereas H. nipponica retained the features of a subtropical/tropical seagrass, even after adapting to the temperate coastal waters of Korea.  相似文献   

4.
Studies focusing on the effect of invasive species on the genetic diversity of native marine invertebrates remain scant. Here we report diversity among French populations of the intertidal gastropod Ocenebra erinacea (Linnaeus, 1758) sampled in the presence and absence of the invasive Ocenebra inornata (Recluz, 1851). Between 1999 and 2004, a total of 352 individuals of O. erinacea was collected from 15 sites (five of which had the invasive present) and was genotyped at the mitochondrial locus Cytochrome Oxidase 1 (cox1). No statistical difference was observed between polymorphism levels recorded within native populations exposed to the invasive, compared with populations sampled in the absence of O. inornata. No sign of native population decline was detected in response to the invader. While significant shifts in native O. erinacea population sizes have previously been reported in the literature, genetic effects may take longer to accumulate, or may be undetectable without a larger panel of genetic markers. By contrast, large genetic distances and significant population differentiation were recorded between Atlantic and Mediterranean O. erinacea samples, suggesting that these populations have distinct evolutionary histories. Comparison of genetic divergence within the closely related genus Nucella suggests that the Atlantic populations of O. erinacea and those from Thau Lagoon in the Mediterranean may belong to different species or subspecies.  相似文献   

5.
To investigate whether or not regional–temporal patterns of seagrass habitat use by fishes existed at the Ryukyu Islands (southern Japan), visual surveys were conducted in seagrass beds and adjacent coral reefs in northern, central, and southern Ryukyu Islands, in November 2004, and May, August, and November 2005, the northern region having less extensive seagrass beds compared with the central and southern regions. During the study period, the seagrass beds were utilized primarily by 31 species, the densities of some of the latter differing significantly among regions. With the exception of Apogonidae and Holocentridae, all species were diurnal and could be divided into 6 groups based on seagrass habitat use patterns; (1) permanent residents A (10 species, e.g. Stethojulis strigiventer), juveniles and adults living in seagrass beds as well as other habitats; (2) permanent residents B (5 species, e.g. Calotomus spinidens), juveniles and adults living only or mainly in seagrass beds; (3) seasonal residents A (4 species, e.g. Cheilodipterus quinquelineatus), juveniles living in seagrass beds as well as other habitats; (4) seasonal residents B (6 species, e.g. Lethrinus atkinsoni), juveniles living only or mainly in seagrass beds; (5) transients (5 species, e.g. Parupeneus indicus), occurring in seagrass beds in the course of foraging over a variety of habitats; and (6) casual species (1 species, Acanthurus blochii), occurring only occasionally in seagrass beds. Regarding temporal differences, juvenile densities in each group were high in May and August compared with November in each region, whereas adult densities did not differ drastically in each month. For regional differences, juvenile and adult densities of permanent residents A and B were higher in the southern and central regions than in the northern region. Moreover, some seasonal residents showed possible ontogenetic habitat shift from seagrass beds to coral reefs in each region. These results indicated that seagrass habitat use patterns by fishes changed temporally and regionally and there may be habitat connectivity between seagrass beds and coral reefs via ontogenetic migration in the Ryukyu Islands.  相似文献   

6.
应用AFLP分子标记技术首次对澳大利亚、海南岛和菲律宾3个：仲群的共60尾花鳗鲡（Anguillamarmorata）幼鱼样品进行了遗传多样性分析。4对选择性扩增引物共扩增得到180个位点,平均每对引物扩增出45个位点。澳大利亚、海南岛和菲律宾3个种群的多态位点分别为78．33％、79．44％和84．44％,Nei’s...  相似文献   

7.
近几十年来,受到人类活动和气候变化的影响,全球海草床呈现退化趋势,海草床的恢复备受关注。其中,海草种子或幼苗移植由于其对供体海草床破坏和影响较小,并能保证海草的遗传多样性而备受重视。移植区的底质类型是决定海草种子或幼苗移植存活率的重要因子,然而,目前关于热带海草种子萌发和幼苗生长对不同底质类型响应的研究很有限。本研究以热带海草海菖蒲(Enhalus acoroides)种子为研究对象,利用室内模拟实验,分别设置细砂和砂砾底质的处理,探讨不同底质类型对海菖蒲种子萌发和幼苗生长的影响。研究发现,细砂组和砂砾组的萌发率和萌发历期的平均值分别96.3%、3.6 d和95.0%、3.4 d,两个处理组之间差异不显著。萌发后的细砂组海菖蒲幼苗的存活率为97.37%,而砂砾组的幼苗存活率仅为81.58%;另外,海菖蒲幼苗的叶片长度、根长度、叶片生长速率和根生长速率在细砂组均显著高于砂砾组。因此,沉积物粒径的差异对海草种子的萌发率和萌发时间没有显著性影响,但沉积物粒径增大会显著降低萌发后海菖蒲幼苗的存活率和生长速率。因此,未来开展海菖蒲种子或幼苗的野外移植,应选取沉积物粒径较小细砂质区域进行移植,可促进海菖蒲种子或幼苗移植的成活率,提高海菖蒲生态修复的成功率。  相似文献   

8.
Carbonate rock cores drilled on the Kikai Seamount, northern Philippine Sea are examined for better understanding of tectonic history of the northern Philippine Sea. The Kikai Seamount, the summit of which is at 1960 m water depth, is an isolated high on the northwestern part of the Amami Plateau formed by subduction-related arc volcanism, and is situated close to the axis of the Ryukyu Trench in front of the Ryukyu Arc, SW Japan. The seamount is capped with shallow-water carbonates such as coral rudstone. Detailed examinations of lithology, larger foraminiferal assemblages, and Sr isotope composition reveal that the core material comprises Miocene carbonates unconformably overlain by Early Pleistocene carbonates. It indicates rapid subsidence of the Kikai Seamount since the Early Pleistocene. The most probable cause of rapid subsidence is collision and subduction of the Amami Plateau laden with the Kikai Seamount. The rapid subsidence may have started when the western corner of the plateau reached the Ryukyu Trench and began subduction beneath the Ryukyu Arc. The onset of the subsidence is likely to be controlled by a motion change in the Philippine Sea Plate. The latest change in subduction direction from north to northwestward into northwestward to west has been believed to have occurred at 1-2 Ma during latest Pliocene to Early Pleistocene time. The change of direction resulted in the shift from oblique into right-angle subduction of the plate beneath the Ryukyu Arc and also the onset of the collision and subduction of the Amami Plateau.  相似文献   

9.
Marine macrophytes sustain valuable epiphytic biodiversity. Nonindigenous macroalgae may induce changes in composition and structure of epifaunal assemblages and therefore support different assemblages from those associated with native species. In this study, differences in faunal community structure between the introduced fucoid Sargassum muticum and the native seagrass Cymodocea nodosa were tested over a year on an intertidal shallow sandy bottom at the southern introduction front, the El Jadida coastline (NW Morocco). Epifaunal community structure consistently differed between macrophytes through seasons, with more species‐rich assemblages associated with S. muticum than C. nodosa despite comparable abundances. The significantly greater epifauna diversity on S. muticum may be related to its structural complexity. However, the species contributing most to differences in assemblages between both macrophytes, such as Steromphala umbilicalis and S. pennanti, were found on both habitats with temporally varying abundances. Some species‐specific affinities were detected (Stenosoma cf. acuminatum, Elasmopus vachoni, Chauvetia brunnea). Nitrogen, dissolved oxygen, suspended matter and temperature were identified as the best explanatory variables contributing to the observed macroepifaunal patterns. This study provides evidence that S. muticum acts as a favourable and additional habitat for epifaunal species and supports a more diverse epifaunal assemblage in this Moroccan seagrass meadow.  相似文献   

10.
Fauna species living in seagrass meadows depend on different food sources, with seagrasses often being marginally important for higher trophic levels. To determine the food web of a mixed-species tropical seagrass meadow in Sulawesi, Indonesia, we analyzed the stable isotope (δ13C and δ15N) signatures of primary producers, particulate organic matter (POM) and fauna species. In addition invertebrates, both infauna and macrobenthic, and fish densities were examined to identify the important species in the meadow. The aims of this study were to identify the main food sources of fauna species by comparing isotopic signatures of different primary producers and fauna, and to estimate qualitatively the importance of seagrass material in the food web. Phytoplankton and water column POM were the most depleted primary food sources for δ13C (range −23.1 to −19.6‰), but no fauna species depended only on these sources for carbon. Epiphytes and Sargassum sp. had intermediate δ13C values (−14.2 to −11.9‰). Sea urchins, gastropods and certain fish species were the main species assimilating this material. Seagrasses and sedimentary POM had the least depleted values (−11.5 to −5.7‰). Between the five seagrass species significant differences in δ13C were measured. The small species Halophila ovalis and Halodule uninervis were most depleted, the largest species Enhalus acoroides was least depleted, while Thalassia hemprichii and Cymodocea rotundata had intermediate values. Fourteen fauna species, accounting for 10% of the total fauna density, were shown to assimilate predominantly (>50%) seagrass material, either directly or indirectly by feeding on seagrass consumers. These species ranged from amphipods up to the benthic top predator Taeniura lymma. Besides these species, about half of the 55 fauna species analyzed had δ13C values higher than the least depleted non-seagrass source, indicating they depended at least partly for their food on seagrass material. This study shows that seagrass material is consumed by a large number of fauna species and is important for a large portion of the food web in tropical seagrass meadows.  相似文献   

11.
海草床是三大典型的近海海洋生态系统之一,具有极高的生态服务功能。然而,截至2015年我国近海海草资源分布现状尚不明晰,严重制约了我国海草床保护与修复工作的开展。2015～2021年,笔者通过实地调查,借助船只走航、声呐探测、遥感等技术手段,重点对我国近海海草资源的分布面积、种类及主要威胁进行了全面普查,并据此提出我国海草床管理与可持续利用对策。结果表明,我国近海海域海草床面积共为26 495.69hm2,可划分为:温带海域海草分布区和热带-亚热带海域海草分布区;我国现有海草4科9属16种。其中,温带海域海草床面积为17 095.01 hm2,主要分布在辽宁、河北、天津和山东沿海,分布有2科3属5种,以鳗草(Zosteramarina)和日本鳗草(Z.japonica)为优势种,其中唐山乐亭-曹妃甸海草床面积达9 025.56 hm2,是我国面积最大的海草床;热带-亚热带海域海草床面积为9 400.68 hm2,主要分布在福建、广东、广西和海南沿海,分布有4科8属12种,以泰来草(Thalassia hemprichii)、海菖蒲(Enhalus acoroides...  相似文献   

12.
Seagrass beds degraded significantly since the last century on both, global and local scale. The seagrass species Enhalus acoroides (Linnaeus f.) Royle is a common species found in almost all marine ecosystems including bays, lagoons and around offshore islands in tropical regions of the West Pacific. It was shown that genetic diversity is an essential indicator of the conditions of ecosystems. In the present study, microsatellite markers were used to assess the genetic diversity and population structure of six distinct seagrass beds along the coast of the Khanh Hoa Province, Vietnam. The results indicate that the genetic diversity of the populations in the open sea is higher than in the lagoon. Seagrass beds occurring in disturbed sites show reduced genetic diversity. The fixing index value (FST) depicts a relatively high genetic structure among populations. Structure analysis clusters the populations into open sea and lagoon populations and cluster analysis and AMOVA indicate a significant difference between the two groups. There are low but non-significant positive correlations between geographic and genetic distances. The different habitats of the open sea and the lagoon are probably responsible for forming two groups.  相似文献   

13.
The Nansei Islands in the southern Japanese Archipelago have 15 taxa of seagrasses from seven genera within three families. Seagrasses in this region grow on coral sands or coral debris in shallow reefs and on sandy or muddy substrata in the shallow areas of bays and inlets. Certain Halophila species grow in deep water off some islands. Enhalus acoroides only reaches to Ishigaki I. with winter sea water temperature (WST) at 23 °C, while Okinawa I. (WST at 21.6 °C) is the northern biogeographic limit for Halophila decipiens, H. okinawensis, H. major and H. gaudichaudii. Amami‐oshima I. (WST at 20.7 °C) is the northern border for Thalassia hemprichii, H. minor, H. ovalis, Cymodocea serrulata, Cymodocea rotundata, Syringodium isoetifolium, Halodule uninervis and Halodule pinifolia. Halophila mikii the sole seagrass collected from Yakushima I. (WST at 19.3 °C), is of volcanic origin. The distribution of tropical seagrasses in the Nansei Islands is clearly associated with the warm Kuroshio Current, WST and habitat availability. Zostera japonica is the only temperate species occurring in the region. Meadows of Z. japonica, H. ovalis and Halodule pinifolia have disappeared from certain localities in the Archipelago, due probably to human activities and natural siltation.  相似文献   

14.
We determined that growth differences among coral fragments transplanted for restoration were influenced by both source population and environmental factors. In two common garden experiments, storm‐generated fragments of Acropora palmata were transplanted from two source populations in the British Virgin Islands to a restoration site (a ‘common garden’) that lacked A. palmata. In the first experiment, colonies from different sources grew at different rates in the first year after transplanting, suggesting either genetic differences among source populations or enduring acclimation to conditions at the source site. No differences in growth among source populations were detected in the second common garden experiment. To isolate environmental effects on growth, we subdivided fragments from three source populations to create genetically identical pieces that were attached separately at both source and restoration sites. Genetically identical pieces from all source populations grew slightly faster at their source than at the restoration site, implying a subtle home‐site advantage. Overall, our results suggest that matching environmental conditions at source and restoration sites may increase the success of restoration projects.  相似文献   

15.
Seagrass meadows across north-eastern Australia, survive a range of environmental conditions in coastal bays, reefs, estuarine and deepwater habitats through adaptation of a range of structural, morphological and physiological features. The aim of this study was to investigate the influence of spatial features (habitat type, site and depth) and photon flux on the photosynthetic performance of 11 tropical seagrass species. Pulse amplitude modulated (PAM) fluorometry was used to generate rapid light curves from which measures of maximal electron transport rate (ETRmax), photosynthetic efficiency (α), saturating irradiance (Ek) and effective quantum yield (ΔF/Fm′) were derived. The amount of light absorbed by leaves (absorption factor) was also determined for each population. In intertidal habitats many seagrass species exhibited typical sun-type responses with a close coupling of both ETRmax and Ek with photon flux. Photosynthetic performance ranged from minima in Thalassodendron ciliatum to maxima in Syringodium isoetifolium. The absence of a coupling between photosynthetic performance and photon flux in subtidal populations was most likely due to highly variable light climates and possible light attenuation, and hence the photo-biology of estuarine and deepwater seagrasses exhibited photosynthetic responses indicative of light limitation. In contrast seagrass species from shallow reef and coastal habitats for the most part exhibited light saturation characteristics. Of all the variables examined ETRmax, Ek and ΔF/Fm′ were most responsive to changing light climates and provide reliable physiological indicators of real-time photosynthetic performance of tropical seagrasses under different light conditions.  相似文献   

16.
丁旭  齐鑫  尹绍武 《海洋科学》2012,36(5):117-123
通过测定花鳗鲡(Anguillia marmorata)海南群体(HN)和菲律宾群体(PH)共19尾个体的线粒体D-loop基因的核苷酸序列(约1017 bp),分析了花鳗鲡的种群遗传结构。结果表明:A、T、G、C 4种核苷酸的平均含量分别为39.8%、28.3%、12.4%、19.4%,A+T含量(68.1%)明显高于G+C含量(31.8%)。所测序列中存在73个变异位点,共有18个单倍型。其中海南群体的单倍型多样度(Hd)、核苷酸多态性(Pi)、平均核苷酸差异数(k)分别为0.982、0.21577和219.655,而菲律宾群体的单倍型多样度、核苷酸多态性、平均核苷酸差异数分别为1.000、0.26728和271.821,两个群体之间平均遗传距离(P)为0.3203。结果表明2个群体遗传变异较大,菲律宾群体的遗传多样性较海南群体更加丰富。通过构建NJ分子系统树表明2个群体的亲缘关系较近。利用中性检验Tajima’s D(海南群体D=1.35345,P>0.01;菲律宾群体D=0.79220,P>0.01)和Fs(海南群体Fs=3.759;菲律宾群体Fs=2.231)探讨其种群历史,表明花鳗鲡群体进化过程种群数量较为稳定。  相似文献   

17.
The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass (Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km2 of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m− 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m− 2) than seagrass meadows (30.0 g AFDM m− 2). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m− 2 and seagrass meadows 6.9 g AFDM m− 2. As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass.  相似文献   

18.
To elucidate which environmental factors affect lagoonal‐scale sea cucumber distributions in Ishigaki Island, Okinawa, Japan, intertidal and subtidal areas of three coral reef lagoons were classified into several ground divisions by bottom characteristics, and sea cucumber densities therein were compared with the composition of sediment cover, grain size and organic content, and coverage of macroalgae, seagrass, and massive corals. Holothuria atra, Holothuria leucospilota, Stichopus chloronotus, and Synapta maculata had highest densities in the nearshore areas but were rare in reef flats, probably because of wave disturbance and low areal cover of sand sediment as potential feeding environments. No relationship was observed between sea cucumber densities and sediment organic content or grain size. Thus, even if these sea cucumbers have selectivity for habitats with a high sediment organic content, the effect of such selectivity on the distribution seems to be limited to relatively small areas. The sea cucumber distributions can be classified by bottom sediment/biota composition into bedrock (H. leucospilota), sand (H. atra), and lagoonal types (St. chloronotus and Sy. maculata). These habitat selections were possibly related to various aspects of sea cucumber ecology such as refuge from predators or turbulence, or settlement and nursery place, which have implications for importance of the complexity of lagoonal‐scale topography and sediment/biota conditions for the coexistence of various holothurian species.  相似文献   

19.
The genetic diversity and variation of three pseudo‐species of the commercially important Indian conch Turbinella pyrum from the southeast coast of India were studied. A total of 88 individuals was genotyped at 12 loci and differences in the genetic diversity among genetic groups were correlated with known population histories. The study identified 535 alleles and all the studied loci were highly polymorphic. The number of alleles ranged between four and 29 with a global mean of 14.861. The global means of the observed and expected heterozygosities were 0.774 and 0.891, respectively. The estimated within‐population inbreeding value (FIS = 0.131) indicated a shortfall of heterozygosity in the populations. An analysis of molecular variance showed that 5% of the total variation was due to differences between genetic groups. The Bayesian approach revealed strong distinctiveness in the three genetic groups studied. Overall microsatellite analysis revealed less genetic diversity in all studied genetic groups and significant genetic variation among the three pseudo‐species. The study highlights the significant distinctiveness of the pseudo‐species of T. pyrum and the need for appropriate conservation efforts in order to prevent further losses of their genetic diversity.  相似文献   

20.
We conducted a field experiment to assess the response of phytal harpacticoids to nutrient‐driven increases of epiphyte load in Posidonia oceanica meadows. First, we evaluated differences in species richness, diversity and assemblage structure of phytal harpacticoids in P. oceanica meadows with differing epiphyte loads. Secondly, we conducted a field experiment where epiphyte load was increased through an in situ addition of nutrients to the water column and evaluated the responses of the harpacticoid assemblages. We predicted that there would be changes in the harpacticoid assemblages as a result of nutrient‐driven increases of epiphyte load, and that these changes would be of a larger magnitude in meadows of low epiphyte load. Our results show that the harpacticoid fauna (>500 μm) present in P. oceanica meadows in the Bay of Palma comprised taxa which are considered phytal and other less abundant ones previously described as sediment dwellers or commensal on other invertebrate species. Nutrient addition had an overall significant effect on epiphyte biomass and on harpacticoid abundance, diversity and assemblage structure, possibly as a response to the increased resources and habitat complexity provided by epiphytes. The abundance of dominant species at each location was favoured by nutrient addition and in some cases correlated with epiphytic biomass, although never strongly. This may indicate that structural complexity or diversity of the epiphytic cover might be more important than the actual epiphytic biomass for the harpacticoid species investigated. More species‐specific studies are necessary to ascertain this and clarify the relationships between harpacticoids and epiphytes in seagrass meadows. To our knowledge, this is the first account of harpacticoid species associated with P. oceanica leaves and the epiphytic community they harbour in the Mediterranean Sea.  相似文献   

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